1. Field of the Invention
This invention relates to methods for separating reactive, usually relatively volatile materials, typically present in relatively small concentrations, from process streams in which they are unwanted.
2. Discussion of the Prior Art
Chemical manufacturing processes frequently produce relatively minor amounts of what may be considered by-products or impurities, which are present in process streams and may result in a variety of problems ranging from UV absorption to discoloration to fouling of equipment. Formation of such materials is particularly troublesome in organic processes, where several materials may be produced as by-products which are difficult to separate from the desired products without expensive supplemental processing. A typical illustration is the unwanted production of carbonyl-containing compounds, which may lead to problems of corrosion, formation of color bodies, formation of polymeric contaminants, and the like. A specific case in point is the formation of aldehydes, including formaldehyde and higher molecular weight aldehydes, in the process for manufacturing alkylene oxides by the catalytic oxidation of alkenes.
Even though it is highly desirable to economize and simplify the relevant manufacturing processes, commercial processes nevertheless resort to complex and expensive distillation and comparable techniques to remove the unwanted materials. If such materials appear in the finished products, they must be either removed by costly post-manufacturing processing, or the products must be recycled or sold as off-specification or lower grade products. Moreover, such post-treatment procedures are undesirable because they may introduce different impurities into the product, which may have negative consequences in certain uses of the product. While various chemical reactions are known for the conversion of, e.g., formaldehyde to less volatile materials, no such reactions appear to have been heretofore incorporated directly into manufacturing processes. Accordingly, the present invention provides a technique of wide applicability whereby relatively volatile by-product materials are reacted in situ to form less volatile derivatives which can be readily separated by simple, relatively inexpensive means from the process streams in which they are found.